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71.
72.
Potential activities of enzymes involved in N,C, P and S cycling in boreal forest soil under different tree species 总被引:1,自引:0,他引:1
The aim of this study was to compare the potential activity of enzymes involved in N, C, P and S cycling in the humus layer under three tree species: silver birch, Norway spruce and Scots pine. For arylsulphatase and protease the highest activities were found under birch, whereas beta-glucosidase activity was highest under pine. Beta-glucosaminidase and acid phosphatase showed similar activities regardless of tree species. Our studies show that soils under these species may differ enzymatically from each other. Enzyme activity studies under different tree species need more attention as the activity of different enzymes influences on soil nutrient availability in boreal forest soil. 相似文献
73.
Pertti J. Martikainen 《Soil biology & biochemistry》1985,17(3):363-367
Nitrification was inhibited by ammonium sulphate and potassium sulphate added to soil from the organic horizon (pH 4.7) of a Myrtillus-type pine forest. Urea did not inhibit nitrification. Soil pH was slightly decreased by the salts but increased by urea. The salts increased soil electrical conductivity more than urea did. The inhibition of nitrification following salt treatments was probably due to a decrease in soil pH and not to osmotic effects. In acid conditions, the salts had a less inhibitory effect on CO2 production than on nitrification, indicating that nitrifying bacteria were more sensitive than other organisms to the salts. 相似文献
74.
Methane oxidation in boreal forest soils: kinetics and sensitivity to pH and ammonium 总被引:1,自引:0,他引:1
In soil incubation experiments we examined if there are differences in the kinetic parameters of atmospheric methane (CH4) oxidation in soils of upland forests and forested peatlands. All soils showed net uptake of atmospheric CH4. One of the upland forests included also managed (clear-cut with or without previous liming or N-fertilization) study plots. The CH4 oxidation in the forested peat soil had a higher Km (510 μl l−1) and Vmax (6.2 nmol CH4 cm−3 h−1) than the upland forest soils (Km from 5 to 18 μl l−1 and Vmax from 0.15 to 1.7 nmol CH4 cm−3 h−1). The forest managements did not affect the Km-values. At atmospheric CH4 concentration, the upland forest soils had a higher CH4 oxidation activity than the forested peat soil; at high CH4 concentrations the reverse was true. Most of the soils oxidised CH4 in the studied pH range from 3 to 7.5. The pH optimum for CH4 oxidation varied from 4 to 7.5. Some of the soils had a pH optimum for CH4 oxidation that was above their natural pH. The CH4 oxidation in the upland forest soils and in the peat soil did not differ in their sensitivities to (NH4)2SO4 or K2SO4 (used as a non-ammonium salt control). Inhibition of CH4 oxidation by (NH4)2SO4 resulted mainly from a general salt effect (osmotic stress) though NH4+ did have some additional inhibitory properties. Both salts were better inhibitors of CH4 oxidation than respiration. The differences in the CH4 oxidation kinetics in the forested peat soil and in the upland forest soils reveal that there are differences in the physiologies of the CH4 oxidisers in these soils. 相似文献
75.
Nitrous oxide emissions were studied with a static chamber technique during 2 years from a drained organic soil in eastern Finland. After drainage, the soil was forested with birch (Betula pendula Roth) and 22 years later, part of the forest was felled and then used for cultivation of barley (Hordeum vulgare L.) and grass. The annual N2O emissions from the cultivated soil (from 8.3 to 11.0 kg N2O-N ha−1 year−1) were ca. twice the annual emission from the adjacent forest site (4.2 kg N2O-N ha−1 year−1). The N2O emissions from the soils without plants (kept bare by regular cutting or tilling) were also lower (from 6.5 to 7.1 kg N2O-N ha−1 year−1) than those from the cultivated soil. There was a high seasonal variation in the fluxes with a maximum in spring and early summer. The N2O fluxes during the winter period accounted for 15-60% of the total annual emissions. N2O fluxes during the snow-free periods were related to the water table (WT) level, water-filled pore space, carbon mineralisation and the soil temperature. A linear regression model with CO2 production, WT and soil temperature at the depth of 5 cm as independent variables explained 54% of the variation in the weekly mean N2O fluxes during the snow-free periods. N2O fluxes were associated with in situ net nitrification, which alone explained 58% of the variation in the mean N2O fluxes during the snow-free period. The N2O-N emissions were from 1.5 to 5% of net nitrification. The acetylene blockage technique indicated that most of the N2O emitted in the snow-free period originated from denitrification. 相似文献
76.
Nitrous oxide emissions from agricultural soils at low temperatures: a laboratory microcosm study 总被引:1,自引:0,他引:1
We studied in laboratory microcosms (intact soil cores) N2O and CO2 emissions from four different agricultural soil types (organic soil, clay, silt and loam) at low temperatures with or without freezing-thawing events. When the temperature of the frozen soil cores was increased stepwise from −8 °C the N2O emissions began to increase at −0.5 °C, and peaked at −0.1 °C in the organic, clay and silt soils, and at +1.6 °C in the loam soils. However, a stepwise decrease in soil temperature from +15 °C also induced an increase in the N2O emissions close to the 0 °C. These emissions peaked between −0.4 and +2.5 °C depending on the soil type and water content. However, the emission maxima were from 2 to 14.3% of those encountered in the experiments where frozen soils were thawed. Our results show that in addition to the well-documented thawing peak, soils also can have a maximum in their N2O emission near 0 °C when soil temperature decrease. These emissions, however, are less than those emitted from thawing soils. The correlations between the N2O and CO2 emissions were weak. Our results suggest that N2O is produced in soils down to a temperature of −6 °C. 相似文献
77.
The inverse of the relative increment rate of size is proposed as a measure of the maturity of a forest tree. The heartwood content within bole cross sections is modeled semiempirically using asymptotic fitting. It is shown that the present proposal for a definition of maturity statistically explains heartwood content far better than age or size. The heartwood content appears to be independent on growth rate and tree size. 相似文献
78.
Norway spruce dust was impregnated with aqueous solutions of chromated copper wood preservatives. Immediately after treatment,
observation of CO2 evolution and O2 consumption were performed. Significant quantities of CO2 were released during reaction of chromium (K2Cr2O7) containing solutions with wood or brown rotted wood. Nevertheless, during reaction of cellulose with these preservatives
we did not observe evolution of CO2. The presence of copper did not influence on concentration of CO2. Opposite to CO2 evolution, treatment of wood and brown rotted wood resulted in O2 consumption. The oxygen concentration decrease in the measuring chamber was approximately 5 times greater than increase of
concentration of carbon dioxide. Electron paramagnetic resonance (EPR) observations of chromium fixation showed that chromium
is reduced from Cr(VI) to Cr(III) with Cr(V) as an intermediate on wood, brown rotted wood and cellulose. However, the reduction
on wood and brown rotted wood was faster than the reduction on cellulose, as determined from changes of Cr signals in EPR
spectra. So, evolution of CO2 and consumption of O2 as well as EPR signals of Cr species thus indicate that brown rotted wood, consisting of lignin and hemicelluloses in contact
with Cr(VI) reacts more intensively than cellulose, and possibly, oxidation mechanisms of lignin and cellulose with Cr(VI)
are different.
Received: 20 July 2000 相似文献
79.
The ambrosia beetle Gnathotrichus materiarius, which originally came from North America, was discovered in southern Finland in 1996. In 1997, using Norwegian drainpipe traps baited with pheromones of Gnathotrichus retusus and G. sulcatus, we collected beetles in the region where the first specimen had been caught in order to determine whether this potential pest species had become established in the area. Samples from a total of 16 traps included 79 species of beetles and 719 individuals, but no specimens of G. materiarius. The most abundant species in the samples were the ambrosia beetles Xyleborus dispar and Trypodendron lineatum. Several predators and other associates of bark beetles were also captured. The majority of the beetles caught were saproxylic species. 相似文献
80.
Methodology comparison for slope correction in canopy leaf area index estimation using hemispherical photography 总被引:1,自引:0,他引:1
The slope effect and correction methods for estimation of canopy gap fraction, leaf area index (LAI), mean leaf angle and clumping index using hemispherical photography, were investigated. The evaluation was carried out in tropical cloud forest and plantations in South-East Kenya in order to consider a range of canopy architecture and slopes up to 65%. The aim was to compare two acquisition techniques and various correction procedures. All estimates assume uniform slope, canopy parallel to ground and homogeneous canopy structure at the photo site level.
- (1) Photographs oriented to local zenith (levelled acquisition). Calculation and removal of sky parts of the hemisphere obstructed by topography. Azimuthal inversion of gap fraction without prior averaging, deriving local LAI estimates (quasi-random model). (i) Fixed path lengths over azimuths. Zenith reference axis. LAI referred to horizontal and corrected for topographic shading. (ii) Variable path lengths over azimuths. Normal to slope reference axis. LAI adjusted to horizontal by dividing by the slope cosine.
- (2) Photographs oriented parallel to slope (tilted acquisition). Fixed path lengths over azimuths. Normal to slope reference axis. LAI adjusted to horizontal by dividing by the slope cosine. Azimuthal inversion of gap fraction without prior averaging, deriving local LAI estimates (quasi-random model).